The Lost City - For Whom the Bell Tolls
Cut down 5 bells.
The first bell is easy to find. Check the top level of the building you zip down to when entering the town.
From the platform with Bell #1, look northeast to spot the next bell in the building across the street.
This is in the first place you probably thought to look: the belfry of the large tower at the north end of town.
On a rooftop in the middle of town.
You can get this once you're sent to commandeer the trebuchet. From the platform, look toward the edge of the map. Shoot through the metal barrier there to open a small room that houses the final bell.